In silico screening of zeolite membranes for CO₂ capture

Abstract

The separation of CO₂/H₂, CO₂/CH₄, and CO₂/N₂ mixtures is of practical importance for CO₂capture and other applications in the processing industries. Use of membranes with microporous layers of zeolites, metal-organic frameworks (MOFs), and zeolitic imidazolate frameworks (ZIFs) offer considerable promise for use in such separations. In view of the extremely wide variety of available microporous structures, there is a need for a systematic screening of potential candidates in order to obtain the best permeation selectivities, Sperm. The permeation selectivity is a product of the adsorption selectivity, S_ads, and the diffusion selectivity, S_diff, i.e. S_perm = S_ads x S_diff. For maximizing S_perm, we need to choose materials for which S_ads and S_diff complement each other. For a wide variety of zeolites, we have used Configurational-Bias Monte Carlo (CBMC) simulations of mixture adsorption isotherms, along with Molecular Dynamics (MD) simulations of diffusivities for three binary mixtures, CO₂/H₂, CO₂/CH₄, and CO₂/N₂, to calculate S_ads, S_diff, and S_perm. These simulation results provide insights into the influence of pore size, pore topology and pore connectivity that influences each of the three selectivities. In particular, we emphasize the important role of correlations in the diffusion behaviors within microporous materials. Furthermore, we have constructed Robeson plots for each of the separations in order to provide generic guidelines to the choice of materials that offer the appropriate compromise between S_perm and the membrane permeability.